Problem with gravity and masses

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hi guys,

I was playing around with Newton Equation F=Gm1m2/r^2

I separate Fr^2 = Gm1m2 . This is bugging me. Fr^2 is a constant for a given 2 bodies(i call Z) of masses. That means that no matter what the distance r in between the two bodies, Z doesn't change. So i take my thought alittle further. Suppose the two bodies are almost infinite small with say ... 5 and 10 mass. so Z value is 50G. Since no matter how close u put them together, the value Z doesnt' change. I put them so close together that they almost like 1 body with a total mass of 15mass. Now I imagine what if they are 7 and 8 mass. The Z value is 56G. I put them throught the same process and let them come so close together that they're almost 1 body with 15mass. Now it looks like I have two identical bodies with different Z value. It seems disturbing.
 

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  • #2
olgranpappy
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but "Z" doesn't mean anything unless the bodies are seperated and if you seperate them in two different ways it shouldn't be surprising that you get two different "Z values".
 
  • #3
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I guess the question is... what does Z means. lol I imagine r^2 as a square and F go up and down to have a constant volume. Though I don't know what it means, but it seems unique.
 
  • #4
olgranpappy
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I guess the question is... what does Z means. lol I imagine r^2 as a square and F go up and down to have a constant volume. Though I don't know what it means, but it seems unique.
it doesn't mean a thing besides G*M_1*M_2... which has only one value for a given M_1 and M_2 but may be different for different values of M_1 and M_2... even when M_1 + M_2 =M_tot is fixed, as you see in your example. but that, too, is meaningless.
 
  • #5
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it doesn't mean a thing besides G*M_1*M_2... which has only one value for a given M_1 and M_2 but may be different for different values of M_1 and M_2... even when M_1 + M_2 =M_tot is fixed, as you see in your example. but that, too, is meaningless.

Fine! I'll keep it as an souvenir. lol
 
  • #6
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Z is a function of r. You can't say that Z is independent of r...basically, when r changes, Z changes. It's just like saying that y=Gx^2 but y doesn't change while x can, it's just completely nonsensical.
 
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